1. Field of the Invention
The present invention relates to improvements in or relating to the production of a precision plastic filter with a meshed net and a frame.
The meshed filter has diverse applications, including a filter or sieve for gasoline or oil using in a car or fan heater, a dust collector filter for air conditioner, a grille cover for speaker or earphone, a strainer for tea or coffee, a supporter for the human body, a grip cover for golf club or bat and other various filtration.
2. Description of the Related Prior Art
The manufacture of narrow pitch nets by conventional injection molding methods was impractical because it was difficult to distribute plastic resin material uniformly over the entire die during the injection molding process.
In the past, a net and a surrounding plastic frame were molded and produced, separately, and then the net was cut and fitted on the frame, followed by insert molding by a skilled worker.
The net and frame of the plastic filter would not be molded into a single and integral unit through one process of molding unless the net structure permits smooth and even injection and distribution of plastic molding material throughout the entire die.
For a conventional molding method, it was impossible to produce a plastic filter having a net and frame in an integral unit through a single process, because there was no means to establish a high pressure enough to inject and distribute plastic material into the die and because the conventional injection molding method then injected the material with high pressure into the narrow net grooves and frame groove, separately. Although not shown or suggested in drawings, the drawbacks of the above prior art are as follows:
(1) Where low-cost equipments or apparatuses are used to inject the plastic material into net rib grooves by low pressure, it is likely that there would be some of the net ribs missing especially at distant locations in the die from a center injection opening or the material may not reach frame grooves. With a smaller pitch of the ribs, it is more difficult to make a filter with an integral formation or structure of the net and frame.
(2) If high pressure injection is used there would be no ribs missing but it needs expensive equipments. Provided however the pressure applied to the plastic material is excessive, the plastic material flowing over in the die would close the meshes of the net.
The object of the present invention is to solve the above discussed drawbacks of the prior art injection molding method.